The first thing that annoyed me was that you need to read the manual to handle the thing. There are cryptic letters and numbers on the display that reveal in what tuning mode and frequency you are using it. I have accidentally mistuned instruments because I was in the wrong tuning mode without understanding it. I want a tuner to be more intuitive than this.
The second thing is the extremely poor build quality. It fell (lightly) on the floor, and one of the two microswitches, which are stupidly placed on the rim, immediately broke. So now I can't turn it on.
I have got a number of different tuners, of which several are clip-on devices (lying around in different instrument cases), and this was the crappiest one.